Take the time to hike into Bryce Canyon. Looking at the scenery from the paved overlooks is nice, however, getting down into the canyon and experiencing the hoodoos, fins, spires, slot canyons, and colors up close is mind blowing. 360 x 360 kaleidoscope.
Zion is nice, and there is more to the park than the main canyon. We really liked the Kolob Terrace area. The main canyon was filled with people -- no solitude at all. You could not get away from the crowds, while the trails elsewhere in the Park were completely empty. We hiked for miles without seeing another soul.
Kodachrome basin state park may be worth a quick side trip, not worth any extended visit IMHO. The Petrified Forest State park may be worth a stop and do the hike to see the logs, if you have time. The National Park in AZ is far larger with a greater variety of petrified logs.